Beam-Squint-Aware Statistical Reconfigurable Intelligent Surface Beamforming Under Amplitude-Phase-Frequency Coupling for Dual Wideband Channels

In this paper, the amplitude-phase-frequency coupling (APFC) constraint in practical reconfigurable intelligent surfaces (RISs) is first investigated. Building on this, three distinct beam-squint-aware and APFC-aware statistical quantized RIS designs are proposed for frequency-and spatial-wideband (dual-wideband) RIS-aided massive multiple-input multiple-output systems, optimized respectively for signal-to-noise ratio, mean statistical mutual information, and the ergodic capacity upper bound based on the cascaded channel covariance matrix.To optimize these metrics, an iterative alternating optimization (AO) algorithm, referred to as the iterative phase refinement algorithm, is adopted, which converges in just a few iterations. Simulation results show that the proposed RIS beamforming designs outperform conventional approaches in terms of spectral efficiency and outage capacity.